The Art of R Programming

General List Operations

Now that you’ve seen a simple example of creating a list, let’s look at how to access and work with lists.

List Indexing

You can access a list component in several different ways:

> j$salary
[1] 55000
> j[["salary"]]
[1] 55000
> j[[2]]
[1] 55000

We can refer to list components by their numerical indices, treating the list as a vector. However, note that in this case, we use double brackets instead of single ones.

So, there are three ways to access an individual component c of a list lst and return it in the data type of c:

• lst$c

• lst[["c"]]

• lst[[i]], where i is the index of c within lst

Each of these is useful in different contexts, as you will see in subsequent examples. But note the qualifying phrase, “return it in the data ...